Famous Study Guide - Physics Flashcards by Will Schweizer

The detectors used in CT scanners are: 1. 1.Xenon gas ionization chambers 2. Barium fluorohalide plates 3. Scintillation (solid state) 4. Amorphous selenium

1 and 3 only

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In order to decrease the appearance of quantum noise:

a. Decrease display field of view (DFOV)
b. Increase pitch c. Increase milliamperage (mA)
d. Decrease slice thickness

Increase milliamperage (mA)

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In order to attempt to correct a ring artifact the technologist should:

a. Increase milliamperage (mA)
b. Decrease slice width
c. Reduce voxel size d. Perform an air calibration scan

d. Perform an air calibration scan

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In a helical acquisition, Total Volume Scanned is equal to: a. Pitch X Slice Thickness X Total Scan Time

b. Slice Thickness X Reconstruction Interval X Pitch
c. Voxel Size X Slice Thickness X Reconstruction Interval
d. Pitch X Reconstruction Interval X Total Scan Time

a. Pitch X Slice Thickness X Total Scan Time

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Pixel size can be determined by:

a. Voxel size / Slice thickness
b. DFOV / Slice thickness c. DFOV / Matrix size
d. Matrix size / Pitch

DFOV / Matrix size

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In order to change the displayed field of view (DFOV) what is needed?

a. Thin slice thickness b. Raw data
c. Image data
d. Small pitch

Raw data

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What type of artifact may occur in a patient with a metal prosthesis in the field of view? a. Beam hardening streaks

b. Partial volume averaging
c. Tube arcing
d. Ring

Beam hardening streaks

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Which detector has a higher Quantum Detector Efficiency (QDE)?

a. Xenon gas ionization chamber
b. Barium fluorohalide plates c. Scintillation (solid state)
d. Amorphous selenium

c. Scintillation (solid state)

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In order to decrease the appearance of noise, which of the following options should the technologist choose?

a. Increasing pitch
b. increasing slice thickness c. use a soft tissue algorithm
d. use a high pass filter

use a soft tissue algorithm

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Which of the following will improve spatial resolution?

a. Larger voxels b. Larger matrix
c. Increased slice thickness
d. Increased field of view

Larger matrix

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The volume of the voxel is determined by: a. Section width

b. Standard deviation
c. Beam collimation
d. Field of view

Section width

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Long term CT image data can be stored in any of the following places with the EXCEPTION of:

a. PACS b. Computer hard drive (disk)
c. RAID (Redundant Array of Inexpensive Disks)
d. CD-ROMs

Computer hard drive (disk)

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Spatial resolution in CT is affected by each of the following with the EXCEPTION of:

a. Matrix size
b. Slice thickness c. Beam collimation
d. Displayed field of view

Beam collimation

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In order to increase contrast resolution, the technologist can: a. Select a soft tissue algorithm for reconstruction

b. Decrease field of view
c. Increase mA
d. Decrease SNR (signal to noise ratio)

Select a soft tissue algorithm for reconstruction

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The artifact commonly found between the petrous ridges and brain tissue caused by x-ray penetrating bone then traveling immediately through soft tissue is a _________ artifact?

a. Ring b. Cupping
c. Partial volume averaging
d. Anatomical misregistration

Cupping

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How do the couch and tube move during a spiral/helical examination?

a. The couch is advanced 10mm at a time after each single gantry rotation
b. After a single gantry rotation, the couch is advanced the same distance as the individual detector size. (i.e. if detector size is 2.5mm, then the couch will move 2.5mm after each gantry rotation)
c. For every 180 degrees of tube rotation (in the gantry) the couch will move 5mm d. The couch and tube (in the gantry) move continuously, at the same time until the scan is completed

The couch and tube (in the gantry) move continuously, at the same time until the scan is completed

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When many, generally small anatomic structures are contained within a voxel, they will be averaged together and therefore become indistinguishable from one another. This process will result in:

a. Beam hardening streaks b. Partial volume averaging
c. Quantum noise
d. Decreased field of view

Partial volume averaging

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What is an array processor responsible for?

a. Determining section width b. Arithmetic computing for image reconstruction
c. Digitizing the signal collected at the detectors
d. Decreasing visibility of noise

Arithmetic computing for image reconstruction

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Which of the following is NOT a disadvantage of spiral (helical) image acquisition?

a. Effective slice thickness blooming
b. Increased partial volume averaging
c. Increased image noise due to interpolation d. Reduction in contrast resolution

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Reduction in contrast resolution

A mathematical method for taking helical data and converting into and viewing it as axial images describes the process of: a. Interpolation

b. Iterative summation
c. Filtered back projection
d. Fourier transformation

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Interpolation

In order to change the image contrast availability (or the number of shades of gray available for display), the technologist must change the:

a. Window level b. Window width
c. Reconstruction algorithm
d. Low pass filter to a high pass filter

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Window width

A Hounsfield unit represents the: a. linear attenuation coefficient of the tissue scanned

b. total amount of remnant radiation detected
c. amount of radiation absorption of the tissue
d. number of photons that have undergone transmission

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linear attenuation coefficient of the tissue scanned

Spatial resolution can be quantified by determining the:

a. amount of quantum noise
b. standard deviation in a large region of interest (ROI) c. number of line pairs per centimeter visualized
d. standard deviation based on line pairs per millimeter visualized

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number of line pairs per centimeter visualized

The data acquisition system (DAS) is located between the:

a. x-ray tube and the detectors
b. Analog to digital converter (ADC) and the CT computer c. Detectors and the array processor
d. X-ray tube and the array processor

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Detectors and the array processor

The electrical (analog) signal captured by the CT detectors is converted into a digital signal by which component? a. Pre-detector collimators b. High resolution comb c. Analog to digital converter (ADC) d. Amplification electronic system

Analog to digital converter (ADC)

What will allow for faster image reconstruction? a. Smaller matrix b. Smaller voxels c. Smaller pixels d. Decreased noise

Smaller matrix

When acquiring scan data for multiplanar reformations, the technologist should chose: a. Thin, overlapping slices b. Thin, contiguous slices c. Thick, overlapping slices d. Thin, non-contiguous slices

Thin, overlapping slices

Anatomical mis-registration can occur due to: a. Section width being too thin for the anatomical part b. Inconsistent patient breath-holds in SSCT c. A large pitch in helical scanning d. Undersampling in the z-axis

Inconsistent patient breath-holds in SSCT

The amount of image noise is quantified in CT using: a. Modulation transfer function b. line pairs per millimeter measurements c. Standard deviation measurements d. Varying size region of interest measurements for comparison

Standard deviation measurements

The range for CT number accuracy of water phantom testing should vary no more than: a. +1 to -1 b. +3 to -3 c. +10 to -10 d. +50 to -50

b. +3 to -3

Which dose measurement is used to describe contiguous sections in CT? a. Dose-length product (DLP) b. Multiple Scan Average Dose (MSAD) c. Slice Sensitivity Profile (SSP) d. Computed Tomography Dose Index (CTDI)

d. Computed Tomography Dose Index (CTDI)

In order to actually decrease the amount of image noise, the technologist should: a. Increase tube current b. Choose a soft tissue algorithm c. Use a wide window width d. Choose a high pass filter

a. Increase tube current

To visualize a graphical representation of spatial resolution, one would use: a. The modulation transfer function b. Line pairs per centimeter c. Standard deviation values d. Mean CT number comparisons

a. The modulation transfer function

A straight, longitudinal black line on a scout image is caused by a(n): a. A patient belonging overlooked b. A faulty pre-detector collimator c. Scatter radiation d. A faulty detector

d. A faulty detector

What is the function of the array processor? a. Defines slice width in MDCT b. Allows window width and level to be altered c. Performs computations necessary for image reconstruction d. Keeps all data in the correct location on the image matrix

c. Performs computations necessary for image reconstruction

Sudden changes in x-ray beam energy due to anatomical structures acting as “filters” results in: a. A need for increased number of photons b. Cupping artifacts c. Star pattern noise d. Ring artifacts

Cupping artifacts

Which of the following will NOT help to reduce partial volume averaging? a. Decrease field of view b. Decrease pixel/voxel size c. Decrease pitch d. Decrease section width

c. Decrease pitch

When is the tube stationary for a CT scan? a. When performing conventional single-slice CT acquisitions b. During the scout acquisition c. For dual tube equipment d. When choosing high-pass algorithm reconstructions

b. During the scout acquisition

What cannot be changed with retrospective reconstruction? a. Displayed field of view and acquired section thickness b. Scanned field of view and acquired section thickness. c. Reconstruction algorithm and retrospective section thickness d. Scanned field of view and reconstruction algorithm

b. Scanned field of view and acquired section thickness.

The most common filter used to absorb low energy x-ray photons is called the: a. Collimation filter b. High resolution comb c. Flat panel filter d. Bow tie filter

d. Bow tie filter

What is the term used to describe the process of using a kernel or algorithm during the filtered back projection reconstruction process? a. Array processing b. High-pass filtration c. Convolution d. Contrast resolution

c. Convolution

What converts light to an electric signal in a scintillation detector? a. Photodiode b. Tungsten plate c. Phosphor d. Central collecting electrode

a. Photodiode

A CT system’s ability to differentiate objects with minimal differences in tissue is termed? a. Low contrast resolution b. High contrast resolution c. Low spatial resolution d. High spatial resolution

a. Low contrast resolution

Which of the following phosphors caused a problem with afterglow in scintillation detectors? a. Bismuth Germinate b. Cadmium Tungstate c. Sodium Iodide d. Rare Earths

c. Sodium Iodide

What represents the average CT number in a Region of Interest (ROI) measurement? a. Standard deviation b. Mean c. Modulation transfer function d. Hounsfield unit

b. Mean

The artifact associated specifically with MDCT that is corrected by an algorithm during the reconstruction process is the ________ artifact. a. Cupping b. Ring c. Streak d. Cone beam

d. Cone beam

Famous Study Guide - Physics Flashcards

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